It is known that in envelope-filling machines, sheaves of sheets of paper or in general of printed materials are prepared along a conveyor line, on which devices are arranged to distribute the sheets or printed materials which have to be piled one on top of the other to constitute the sheaves.
Thus formed, the sheaves must then be transferred to a station of the machine, where they are inserted into respective envelopes which are suitably positioned and held open to facilitate the operation.
At times, when using window envelopes for example, when the sheaf must also include a sheet bearing an address, the sheet bearing the address is situated on the opposite side relative to the side of the envelope containing the window. This may be caused by a particular order of deposition of the sheets along the preparation line, which order may in such cases be unavoidable.
For example, the first distributed sheet may bear a bar code indicating how many and which sheets must subsequently placed one on top of the other. The code must be readable by a bar code reader, and must therefore face downwards so as not to be covered by subsequent sheets.
For constructional and functional reasons, known to persons skilled in the art, on a same machine the envelopes must always be supplied to the envelope-filling station with the same orientation, so that in the case mentioned, it becomes necessary to overturn the sheaf in order for the sheet bearing the address, which also bears the bar code, to be situated on the window side of the envelope.
To this end, a linking conveyor is usually provided between the preparation line and the envelope-filling station. Along the conveyor there is an overturning device, which, after receiving the sheaf, rotates it by 180°, then restoring the sheaf to the advancement direction towards the envelope-filling station.
The sheaf-overturning device can operate in two different ways. In the first, the sheaf is halted at a section rotating around a transversal axis to the advancement direction, and which generally coincides with one end of the sheaf. In the second, the sheaf is halted at a section which rotates around an axis which is parallel to the advancement direction, generally arranged along the centre line thereof.
The constructional and operational complexity of a device such as the one described above is self-evident.
Equally evident are the drawbacks associated with this type of conveyor, where transfer to the overturning device increases the risk of jamming, in addition evidently to slowing down operations.
Linking conveyors are known which are specially designed for transferring sheaves of paper or other printed materials from one operating station of a same machine to another, or from one machine to another. These devices are constituted by two belt conveyor devices, arranged one above the other. A problem with these known conveyor devices is constituted by the sheaf input and output sections of the linking conveyor. In these sections, in fact, the position of the rollers of the lower conveyor coincides with that of the rollers of the upper conveyor, along shared tangential lines.
As the device has to handle sheaves having different thicknesses, in order to avoid laborious adjustment operations and allow the device to operate without having to stop whenever the thickness varies, the bearing rollers of the upper conveyor are each mounted on a vertically mobile element, upon which springs act, pushing the element towards the corresponding lower roller.
In this way, the roller is positioned for the minimum predetermined thickness for the sheaves, and when the sheaf increases in thickness, the roller is elastically displaced, thus allowing passage of the thicker sheaf. Subsequently, the springs reposition the roller in the selected position.
Although simple, this solution nevertheless impacts negatively on construction costs, in addition to requiring greater maintenance on organs which need to be able to move constantly without hindrance so as to enable the sheaves to pass with ease.